The present invention relates to nuclear magnetic resonance (NMR) techniques, and in particular to field cycling spectrometry.
Field cycling relaxometry is an extremely powerful NMR technique for studying molecular dynamics within a sample or object under analysis. In field cycling, the dependence of the longitudinal relaxation time T1(xcfx890) on spectrometer frequency xcfx890 is typically determined over frequencies ranging from 0.01 to 10 MHz. It is called field cycling because the spectrometer frequency is related to the magnetic field strength as xcfx890=xcex3B0 where xcex3 is the proton gyromagnetic ratio. The frequency dependence of T1 is therefore determined by rapidly cycling through different field strengths, B0.
Commercial availability of field-cycling spectrometers is strictly limited at the present time. There are several reasons for this slow commercialization of field cycling spectrometers. Firstly, relaxation times can be as short as a few milliseconds, so it is necessary to be able to switch magnetic field strengths very rapidly while maintaining field homogeneity. This requires very efficient magnet cooling and a special power supply capable of delivering high power (ca. 15 kW) very rapidly. This makes such equipment both complex and expensive.
An alternative approach to field cycling is to mechanically shuffle the sample between high and low magnetic fields. This has the advantage that rapid field switching is not required. However, known applications of this idea are based on linear translation of the sample in a back-and-forth movement between magnetic fields. This is mechanically demanding and also very Slow, so that short T1 values cannot be measured. The NMR acquisition is also made when the sample is stationary within the magnetic fields, so that a time delay is necessary to allow mechanical vibrations to damp down before acquisition can begin.
The present invention seeks to provide a field cycling NMR spectrometer which overcomes some or all of the problems of the prior art as enumerated above.
According to one aspect, the present invention provides an apparatus for making nuclear magnetic resonance measurements on an object, comprising:
means for conveying the object under analysis, at predetermined angular velocity, successively through a first, spatially characterized, constant magnetic field B0 and a second, spatially characterized, constant magnetic field Bs; and
means for detecting nuclear magnetic resonance signals weighted with at least one nuclear magnetic resonance parameter from said object.
According to a further aspect, the present invention provides a method of making nuclear magnetic resonance measurements on an object under analysis, comprising the steps of:
rotating the object at a first predetermined angular velocity about a point so that the object is repeatedly conveyed along a circular path, which circular path sequentially passes through a first magnet having a first, spatially characterized, constant field strength B0 and a second magnet having a second, spatially characterized, constant field strength Bs; and
detecting nuclear magnetic resonance signals weighted with at least one nuclear magnetic resonance parameter from said object after said at least part of an object passes through said second magnet.